Temperature compensated crystal holder



Feb. 24, 1942. J. B. ATWOOD TEMPERATURE COMPENSATED CRYSTAL HOLDER Filed Nov. 24, 1939 l /3 11g? 4? r 7 9 r%g %iufillllim g D ll mm? I INVENTOR.

JOHN B. ATWOOQ BY ATTORNEY.

Patented Feb 24, 1942 TEMPERATURE COMPENSATED CRYSTAL HOLDER mm Boyd Atwood, River-head, N. 11., a'ssignor to Radio Corporation of America, a corporation of Delaware Application November 24, 1939, Serial No. 305,912-

(Cl. 1 7l--327) 6 Claims.

A feature of this invention is the selection oi! material for the electrode spacers from the same sion, however, if the spacers are combined 'to make a single composite spacer and also by suitable proportion of thickness no variation of the piece of quartz and also cutting it at the same The most common cause bf this air gap will occur,

This invention will best be understood by referring to the accompanying drawing,'in which:

Fig. 1 shows a crystal holder with composite jfused quartz and angle quartz spacers;

Fig. 2 is a plan view of a preferred embodiment of this invention with the cover and binding members removed, in which the spacers and holder are proportioned to give substantially complete temperature compensation; and

Fig. 3 is'a cross sctional view of the entire holder. I

Referring now in detail to Fig. 1 of the ,drawing, the crystal I is shown restingupon the bottom electrode 2 with the top electrode 3 spaced .to' give the desired air gap by means of two and contractions of the crystal holder parts can be compensated, an improvement in crystal stability will be obtained.

In thepast, various types of temperature comquartz spacers, the top spacer I being that of fused quartz and the bottom spacer 5 being that q of angle quartz, which is made from the same required results. Such type of crystal holders are generally expensive to build, bulky and rather cumbersome to adjust.

This invention compensates for the undesir same as the well-known types of crystal holders 1 piece of quartz as crystal I and likewise cut to have the same thickness and also cut at the same angle. It will be seen by this arrangement that there will be very little change in the air gap with temperature as there is left only a thin fused quartz spacer of low coeficient of expansion.

The preferred embodiment of. this invention is shown by Figs. 2 and 3, in which a more complete holder arrangement is shown. The crystal I is which consist of two electrodes separated by fused quartz spacers,- the spacers being made thick enough to provide the desired air gap.

Bymy invention, the fused quartz spacers are two electrodes separated by fused quartz-spacers that are thick enough to provide an air gap of the desired thickness have a temperature coemcient of expansion of 0.5 l0/C. while .the-

quartz crystal may be from 8 l0-/C." to

13 10- /C., depending upon the angle at which it is cut from the mother crystal. This results in an air gap which will vary with the temperature, due to the different coeflicients of expanv I have found that piezo-electric crystal holders which consist of supported within a base i of the holder. This member, is preferably made of metal, so as,to

serve as the lower electrode of the crystal. An upper electrode 1 is located above crystal I and is supported from a top holder or cover member 8.. Electrode 1 is spaced ,from member 8 by means-01a fused quartz spacer 9 of any convenient thickness. A screw III is threaded into electrode I and has located under its head',a

. spring collar I I arranged to take up difference in various parts.

"expansion; of the assembled parts. The holder top 8 is preferably that of a circular plate and is separated from basetby means of a plurality of composite crystal spacers l and 5, which are of similar material as that mentioned above in con-, nection with Fig. 1. An insulating bushing I2 insulates screw II from short-circuiting members 0, 8 anti, and is also provided with spring washers to take up the difference of expansion of the It will be noted that in order to maintain accurate temperature compensation, the

spacer 5 is ofth same thickness as the quartz crystal I and made from the same piece and likewise cut at the same angle. The dimension D indicated by the arrows on member 6 is that of a compensating dimension which may be of any shape, such as, for example, a rim cut from member 6, a separate ring, or a spacer, and is equal. to the thickness of the top electrode 1, if made of the same material as electrode 1. However, if the materials are different, the dimensions must be proportioned to give the same amount of expansion with temperature for each. The fused quartz 10 spacer 4 is of the same thicknessdimension as quartz spacer 9, except for a slight increase, which increase is the amount of the desired air gap.

If desired, the crystal holder may be surrounded by a thin insulating casing II which is arranged to encircle base 6, and having a height such that it is slightly shorter than th combined height of spacers 4 and 5 and base plate 8.

Although this holder is shown as circular in shape, it is to be understood that it may take anyother shape. Likewise, the spacers 4 and 5 may be substituted by a composite ring of metal and two kinds of quartz which is of the same outside diameter as base member 5. Therefore, this" invention should not be limited to the precise arrangement shown.

What is claimed is:

1. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one of said electrodes having a depressed space equal in depth to the thickness of the other electrode, temperature compensating means including a plurality of spacing members to provide an air gap between said crystal and at least on elec-' trode, one of said spacing members made from the same piece of crystal as said crystal element and having the same thickness, a second quartz. spacing member placed to abut said first mentioned spacing member.

2. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one

of said electrodes acting as a base plate, a cover plate for said holder, temperature compensating means comprising a composite spacing column extending from the electrode which acts as a base plate, said composite column including a metal and at least two different kinds of quartz, the thickness of said column being so proportioned as to maintain the'air gap of said crystal constant. 4 3. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one of said electrodes acting as a base plate, a cover plate for said holder, temperature compensating means comprising a composite spacing column extending from the electrode which acts as a base plate, said column including a metal and at least two different kinds of quartz, the thickness of said column being proportioned to maintain the air gap of said crystal constant, and spring tension means located above said composite column to take up the difference in expansion of the materials of said composite column.

4. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one of said electrodes acting as a base plate, a cover plate for said holder, temperature compensating means comprising a composite ring-like spacing column extending from the electrode which acts as a base plate, said column including a metal" and at least two different kinds of quartz, the thickness of said column being proportioned to maintain the air gap of said crystal constant, a threaded member passing through said composite spacing column, and a spring tension member arranged on said threaded member to take up difference in expansion of the material of said composite column.

5. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one of said electrodes acting as a base plate, a cover plate for said holder, temperature compensating means comprising a composite spacing column extending from the electrode which acts as a base plate. said column including a metal and at least two different kinds of quartz, the thickness of said column being proportioned to maintain the air gap of said crystal constant, a threaded member passing through said composite spacing column, a screw passing through said column, an insular.- ing bushing for insulating said screw from said cover plate, and a spring tension member interposed between said cover plate and the head of said screw to take up the difference in expansion of the materials of said composite column,

a 6. A temperature compensated crystal holder comprising two electrodes, a piezo-electric crystal element interposed between said electrodes, one of said electrodes having a depressed space equal in depth to the thickness of the other electrode, temperature compensating means secured to the electrode which has a depressed space, said compensating means including a plurality of spacing members to provide an air gap between said crystal and the other electrode; one of said spacing members made from the same piece of crystal as said crystal element and having the same thickness, 3. second quartz spacing member placed to abut said first mentioned spacing member.

JOHN BOYD ATWOOD. 

